Composite propellant including gem-nf2-alkyl carborane

ABSTRACT

COMPOSITE PROPELLANTS WITH VERY HIGH BURNING RATES (E.G., BURNING RATES IN THE ARRANGE OF J TO 20 INCHES/SECOND) RESULT WHEN DERIVATIVES OF CARBONARANE (E.G., ALKYLCARBORANES OR GEMINAL NF CARBORANES) ARE INCORPORATED INTO THE PROPELLANT MIXTURE OF THIS INVENTION. PROPELLANTS OF THIS INVENTION, WHICH ARE CONSTITUTED OF A POLYBUTADIENE BINDER (HYDROXY-TERMINATED OR CARBOXY-TERMINATED) AN AKYLCARBORANE BALLISTIC MODIFIER (E.G., N-BUTYLACARBORANE, ISOBUTYLCARBORANE, OR N-HEXYLCARBORANE), A SILOXANYL- OR SILYLCARBORANES (E.G., BIS(PENTAMETHYLDISILOXANYL)-METACARBORANE, 1-N-BUTYL-2-TRIMETHYL-SILYLCARBORANE), OR A GEMINAL NF CARBORANE BALLISTIC MODIFIER, AMMONIUM PERCHLORATE OXIDIZER, METAL ADDITIVE OF ALUMINUM POWDER, PROCESSING AID (E.G., LECITHIN, HEXANE, ETC.), AND A CURING AGENT SELECTED FROM A DIAZIRIDINE OR A TRAIZIRIDINE AND DIISOCYANATE, BURN AT APPROXIMATELY FOUR TIMES THE BURNING RATE OF A CONTROL PROPELLANT CONTAINING NO ALKYLCARBORANE BALLISTIC MODIFIER OR GEMINAL NF CARBORANE BALLISTIC MODIFIER.

United States Patent 01 fice 3,764,417 Patented Oct. 9, 1973 US. Cl. 149-192 SS 5 Claims ABSTRACT OF THE DISCLOSURE Composite propellants with very high burning rates (e.g., burning rates in the arrange of 4 to 20 inches/second) result when derivatives of carborane (e.g., alkylcarboranes or geminal NF carboranes) are incorporated into the propellant mixture of this invention. Propellants of this invention, which are constituted of a polybutadiene binder (hydroxy-terminated or carboxy-terminated) an akylcarborane ballistic modifier (e.g., n-butylcarborane, isobutylcarborane, or n-hexylcarborane), a siloxanylor silylcarboranes [e.g., bis(pentamethyldisiloxanyl)-metacarborane, 1-n-butyl-2-trimethyl-silylcarborane], or a geminal NF carborane ballistic modifier, ammonium perchlorate oxidizer, metal additive of aluminum powder, processing aid (e.g., lecithin, hexane, etc.), and a curing agent selected from a diaziridine or a triaziridine and diisocyanate, burn at approximately four times the burning rate of a control propellant containing no alkylcarborane ballistic modifier or geminal NF carborane ballistic modifier.

BACKGROUND OF THE INVENTION Current high-rate propellants employ randomly oriented aluminum or Zirconium staple. Use of staple complicates propellant processing because of the tendency of fiber to mat, impeding dispersion, and because special casting techniques are necessary to avoid orientation of the fibers along stream lines.

Dicarbaclovododecaborane (carborane) and derivatives of carborane belong to a class of compounds known to be effective ballistic modifiers for obtaining high burning rates. One such derivative of carborane, carboanyl methyl acrylate (CMA), has been converted into a copolymer with acrylic acid units which serve as crosslinking sites for curing propellants made with the copolymer.

Certain derivatives of carborane are needed which can be incorporated into propellants made with polybutadiene binder.

A need exists for non-fiber bearing propellants with very high burning rates in the range of inches/second at 10,000 p.s.i. The increased burning rate achieved by this invention offers several advantages one of which is to provide a desired high burning rate while using a propellant charge having a simpler grain design than the complex grain design normally required to achieve the ultrahigh burning rates for conventional propellants employing staple.

An object of this invention is to provide derivatives of carboranes usable as ballistic modifiers for propellants having polybutadiene as the binder and other conventional propellant ingredients.

Another object is to provide composite propellant compositions which burn at very high rates over a wide range of pressures when derivatives of carborane are employed as the ballistic modifier.

SUMMARY OF THE INVENTION The propellant compositions of this invention contain a ballistic modifier selected from the representative alkyl carboranes, geminal NF carboranes, and siloxanyl or silylcarboranes as follows.

(1 Alkylcarboranes:

(a) R-C--/C-R' io i0 R=hydrogen or alkyl R'=alkyl (b) R-C\ 0 C-CH2(CH2)xCH3 io m 76:1, 2, 3 R=hydrogen. r

(2) Geminal NF carborane:

RC o(cH2),- (CH2)yCH! Bio Hi0 x=1, 2, 3 R=hydrogen or alkyl :0, 1,2,3

(3) Siloxanyl or silylcarboranes:

R R Z-S'iC S i R=alkyl or hydrogen Z=alkyl, hydrogen, chlorine, or oxygen linked silicon structure where R=alkyl or hydrogen Z=alkyl, hydrogen, chlorine, or oxygen linked silicon structure The ballistic modifiers of this invention when used in amounts from about 10 to about 14 weight percent of the propellant composition provide up to 400 percent increase in burning rate as compared to a control propellant containing the same ingredients with the exception that it contained no ballistic modifier.

The high burning rate composite propellants of this invention contain in addition to the ballistic modifier, ammonium perchlorate oxidizer, metal additive of aluminum powder, carboxyor hydroxy-terminated polybutadiene, diaziridine or a triaziridine curing agent (when carboxyterminated polybutadiene is used) or diisocyanate curing agent (when hydroxy-terminated polybutadiene is used), and optionally, processing aid (e.g., lecithin).

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example I, below sets forth two procedures whereby alkylcarborane ballistic modifiers can be produced. Example II below, sets forth the procedures for producing NF carborane ballistic modifiers, vicinal and geminal; the geminal composition is preferred for use in the propellant disclosed later herein. Example III, below, sets forth the general procedure for the preparation of silylcarboranes. Example IV, below, discloses the preparation of fast burning polybutadiene based propellants which employ ballistic modifiers selected from alkylcarboranes, siloxanylor silylcarboranes, and geminal NF carboranes. The cured intimate mixtures are composite propellants which burn at very high rates over a wide range of pressures as set forth in data below under Example III.

EXAMPLE I Synthesis of alkylcarboranes Two general procedures for the synthesis of alkylcarboranes are:

1) By reaction of bis(acetonitrile)decarborane with acetylenes as follows:

( a )2- io ia R-CEC-R R=hydrogen, aliphatic, aromatics, or ester groups.

(2) By reaction of lithiocarboranes with alkyl bromides R=hydrogen, aliphatic, aromatic or ester groups.

Example of route 1.-Bis(acetonitrile)decarborane (0.1515 mole) and 350 ml. of dry toluene are placed in a 3-liter, 3-neck flask equipped with a mechanical stirrer, reflux condenser, thermometer and dropping funnel. The reaction vessel is purged with N and brought to reflux temperature (112 C.). l-octyne (.2265 mole) placed in the additional funnel, is added in portions refluxing 10 minutes after each of the first two additions and for 30 minutes after the last addition. The flask is then cooled, the solvent removed in vacuo, and the residue is extracted with nhexane. The n-hexane solution is then washed with 10% sodium hydroxide in water and then with water. The n-hexane solution is then dried over magnesium sulfate and the solvent removed under vacuum. The residue is then distilled to give n-hexylcarborane (NHC).

in m B.P. 120 C.-1-3 mm. as a colorless liquid. n-Hexylcarborane obtained by this procedure is impure with some unknown species, but may be purified by treating a concentrated acetone solution of the carborane with aqueous chromic acid overnight. The carborane is then extracted out of the acetone-water solution with ether. The ether solution is washed three times with sodium bicarbonate in water. After washing with water, the ether layer is dried over magnesium sulfate, and the solvent removed, under vacuum and the residue distilled. n-Hexylcarborane treated this way is 99% pure by vapor phase chromatog raphy. Other examples of carboranes obtained by this method are n-butylcarborane,

HC B9H.

and isobutylcarborane,

CHI

HC---CCH;CH (IBC) O CHa io Hi A wide range of carboranes can be prepared by choosing the appropriate acetylene.

Example of route 2.-Carborane (5 gms.) and 150 ml. of anhydrous ether are put into a 300 ml. three-neck flask equipped with two addition funnels, a nitrogen inlet and a reflux condenser. The nitrogen purge is started, 21.5 ml. of 1.6 molar butyl lithium is put in one addition funnel and 5 ml. of 5-bromo-2-pentene is placed into the other addition funnel. The butyl lithium is added dropwise to the carborane-ether solution. After the addition is complete, the flask is warmed to reflux and the 5-bromo-2- pentene is added dropwise. The reaction is refluxed for an additional 30 minutes. The flask is then cooled to room temperature and 150 ml. of water poured ito the flask. The ether layer is separated, dried over magnesium sulfate and the solvent removed. The remaining oil is distilled giving n-pentenyl-carborane, B.P. 1l0-13 mm., as a colorless liquid. W a

A wide range of carboranes can be prepared by choosing the appropriate alkyl bromide.

EXAMPLE 11 Synthesis of NF carboranes Two general routes apply for the synthesis of NF carboranes. They are as follows:

Example of route 1.1-isopropenyl carborane (0.011 mole) is washed into a SOO-rnl. stainless steel Hoke bomb with 100 ml. of carbon tetrachloride (Spectrograde). The bomb is cooled to C., evacuated, and charged with tetrafluorohydrazine (0.044 mole). The bomb is heated to 150 C. for 24 hours. Excess tetrafluorohydrazine and carbon tetrachloride are removed under vacuum and the remaining oil distilled to give 1,2-bis(difluoramine)-2-(1- carboranyl propane,

HC-C I 0 NFz NFz NFIPO(vie) io Hm BAP. C.-3 mm., as a colorless liquid in 67% yield. Carboranes containing any alkenyl group may be used to obtain a wide variety of vicinal N-F carboranes.

Vicinal NF carboranes which contain alpha hydrogens may be dehydrofluorinated upon treatment with base to give the corresponding difiuoramino nitrile as given below:

Example of route 2.Methylcarboranylacetone (MCA) (4.009 gms.) and 75 ml. of methylene chloride are placed into a one-neck 300-ml. flask. The flask is then cooled to C. with stirring. Ten ml. of 3 M DFSA in methylene chloride is diluted with 25 ml. more of methylene chloride and added to the solution at 0 C. The flask is stoppered and stirred for 30 minutes. The contents are poured into a separatory funnel and the acid layer drawn off into a beaker of ice. The methylene chloride is removed in vacuo and the remaining oil is chromatographed over silica gel to give NFMCA (gem),

CHKC 0 B10 m as a colorless liquid, DTA exotherm 221-224 C. Any carboranyl ketone can be used to give a geminal NF carborane.

EXAMPLE III The general procedure for the preparation of silylcarboranes is:

R=alkyl, hydrogen x=alkyl, chlorine, hydrogen Z=alkyl, chlorine, hydrogen, or oxygen linked silicon structure.

The reaction procedure is the same as that described in route 2 of Example 1 except that twice as much butyl lithium is added and that 5 ml. of (CH SiCl is added to the lithio salt instead of S-bromo-Z-pentene. The product is then distilled to give the pure silyl carborane.

Oxygen may be introduced into the silylcarborane structure (when Z=chlorine) by reacting the chlorine containing silylcarborane with an alcohol. The resulting siloxanylcarboranes are useful ballistic modifiers.

Representative of the siloxanylcarborane useful as ballistic modifiers of this invention are:

Bis(pentamethyldisiloxanyl)-m-carborane with structures:

and bis(B-phenylhexamethyltrisiloxanyl) m carborane with the structure:

Representative of the silylcarboranes useful as ballistic modifiers of this invention is:

1-(n-butyl)-2-trimethylsilylcarborane with structure:

(I/Ha orn-si-o oormacn,

EXAMPLE IV Preparation of fast burning polybutadiene based propellants (A) Preparation of fast burning propellant with NBC as ballistic modifier.A fast burning composite propellant is produced by incorporating NBC into the propellant mixture as a ballistic modifier. The composition and burning rates obtained with this propellant are as follows.

Component: Wt. percent Ammonium perchlorate (2.5 microns) 79.0 Aluminum (powder) 1.13 Binder (carboxy terminated polybutadiene) 8.30 Diaziridine curing agent 0.93 Lecithin 0.34 Ballistic modifier (NBC) (11 butylcarborane) 10.30

Pressure: Burning rate (in/sec.) 1000 4.0

The burning rate obtained with the ballistic modifier NBC is remarkable, since a control with no ballistic modifier would have a burning rate in the range of about 1.0 in./sec. at 1000 p.s.i. and about 4.0 in./sec. at 10,000 p.s.i.

The propellant is prepared by dispersing about half of the ammonium perchlorate oxidizer in the liquid polybutadiene binder to produce a paste which contains a small amount of the surfactant lecithin to reduce the viscosity of the paste. Next, the ballistic modifier (NBC) is added to the paste at F. followed by aluminum and the remainder of the ammonium perchlorate. The remainder of the ammonium perchlorate and aluminum are added slowly in increments with good mixing between additions in a vertical mixer under vacuum. Finally, the diaziridine curing agent, N,N'-octamethylene-bis-l-aziridine carboxamide, or the triaziridine curing agent tris (methylaziridinyl) phosphine oxide, or the like, is added to the propellant which is given an additional one-hour mix under vacuum at 140 F. The final propellant mixture has a viscosity of about six killopoise at 140 F. and is cast into a mold and cured at 140 F. for about 24 hours. The cured propellant is burned under nitrogen pressure to give the results listed above.

(B) Preparation of a fast burning propellant with NHC as ballistic modifier.A fast burning composite propellant is produced by incorporating NHC into the propellant mixture as a ballistic modifier. The composition and burning rates obtained with the propellant are as follows.

Composition: Wt. percent Ammonium perchlorate- 2.5 microns 34.0

8.0 microns 36.0

Aluminum (powder) 10.0

Binder (carboxy terminated polybutadiene)--- 6.7

Diaziridine curing agent 1.2

Lecithin 0.1

Ballistic modifier (NHC) (n-hexylca1'borane) 12.0

7 Pressure: Burning rate (in/sec.) 1000 3.0 2000 4.4 5000 7.4 10,000 11.0 15,000 14.0

The propellant is prepared using the same procedure described above in Example (A). The slower burning rates are due to the substitution of ammonium perchlorate oxidizer with a larger particle size (8 microns) for part of the fine grind perchlorate (2.5 microns) used in Example (A).

(C) Preparation of a fast burning propellant with IBC as ballastic modifier.--A fast burning composite propellant is produced by incorporating IBC into the propellant mixture as a ballistic modifier. The composition and burning rates obtained with this propellant are as follows.

Component: Wt. percent 1000 3.5 2000 5.2 5000 9.0 10,000 13.0 15,000 17.0

Pressure: Burning rate (in/sec.)

Ammonium perchlorate (2.5 microns) 73.0 Aluminum (powder) 2.0 Binder (hydroxy terminated polybutadiene) 10.6 Diisocyanate curing agent 2.4 Ballistic modifier (IBC) (isobutylcarborane) 12.0

The above noted propellant is mixed by employing an inert, volatile diluent (hexane) as a processing aid. The ammonium perchlorate oxidizer is stirred with hexane solvent to form a slurry. The binder (hydroxy terminated polybutadiene) and ballistic modifier (IBC) are added to the slurry and well mixed at ambient temperature in a vertical mixer. The hexane diluent is stripped from the propellant at 140 F. while mixing is continued under vacuum. After removal of the diluent, the curing agent, a commercial diisocyanate is added to the propellant mixture. The specified curing agent is made from a 36-carbon dimer aliphatic dibasic acid; exact structure is a complex mixture of isomers. A preferred composition of the specified commercial diisocyanate is available as DDI-1410- Diisocyanate from General Mills, Inc. Other aliphatic diisocyanates and aromatic diisocyanates will provide satisfactory curing in the propellant. The propellant is mixed for another hour under vacuum at 140 F. and cast into an appropriate mold for curing at 140 F. for two days. The propellant is removed from the mold and burns at various pressures under nitrogen to give the results shown above.

(D) Preparation of a fast burning propellant with NF- MCA as ballistic modifiers.A fast burning composite propellant is produced by incorporating NF-MCA into the propellant mixture as a ballistic modifier. NF-MCA is the difluoramino derivative of methyl carboranyl acetone. It is soluble in polybutadiene binder. The composition of the propellant made with NF-MCA is as follows.

Component: Wt. percent Ammonium perchlorate (18 microns) 59.4 Aluminum (powder) 14.2 Binder (hydroxy terminated polybutadiene) 13.2 NF-MCA 13.2

The propellant is easy to mix using conventional techniques and requires no special procedures for incorporating the ammonium perchlorate oxidizer. Toluene diisocyanate is added up to about 3 parts per 100 parts of other propellant ingredients tocure the propellant at 140 F. for 16 hours. The burning rate of the cured propellant at 2000 p.s.i. is 4.85 in./sec. The specified burning rate is the highest burning rate obtained in this pressure for a composite propellant made with 18 microns ammonium perchlorate. For example, the NBC modifier used in (A) gives a burning rate of 3.85 in./sec. at 2000 p.s.i. when used in the propellant formulation given above.

The examples provided illustrate that many propellant compositions may be formulated to achieve very high burning rates for specific uses. The compositions may be comprised of an inorganic oxidizing salt (ammonium perchlorate oxidizer being preferred) in amounts from about 5 8 to about weight percent, metal additive of aluminum powder from about lto about 15 weight percent, polybutadiene binder from about 6 to about 14 weight percent, curing agent selected from a diisocyanate and diaziridine in an amount from about 1 to about 3 weight percent; processing aids (e.g. lecithin) in trace amounts, and alkyldecarborane ballistic modifier, a silicon-containing carborane modifier, or a geminal NF carborane ballistic modifier in amounts from about 8 to about 14 weight percent. The ballistic requirements for the propellant system would indicate the preferable compositions to select. The burning rate is increased as the boron content and NF content is increased. The approximate ranges set forth provide optimal benefit for the quantities used in the cured propellant having also very satisfactory physical and chemical properties.

(E) Preparation of a fast burning propellant with silicon containing carborane.-A fast burning composite propellant is produced by incorporating 1-(n-butyl)-2-trimethylsilylcarborane into the propellant mixture as a ballistic modifier. This silicon containing compound as well as other silyl and siloxanyl carboranes is soluble in polybutadiene binder. The composition of the slurry made with these silicon carboranes is:

The propellant was mixed by conventional techniques and required no special procedures. The rates obtained for several silicon carbonane additives are as follows:

Rate, in. /sec. at-- 750 1, 500 Silicon carborane p.s.i. p.s.i.

1-(n-butyl)-2-trimethylsilylcarborane O. 67 1. 01 Bis(pentamethyldisiloxanyl)-m carborane 0. 64 0. 95 Bis(S-phenyihexamethyltrisiloxanyl)-m-carborane. 0. 53 0.

The rates of the control with 5% inert additive (isodecyl pelargonate) instead of the silyl carborane were 0.42 in./ sec. at 750 p.s.i. and 0.74 in./sec. at 1500 p.s.i.

The above formulation may be cured with a diisocyanate. The silicon carborane may be used to replace the Coplasticizer which is optional in use up to about 5 weight percent. A diaziridine or a triaziridine curing agent is used to cure the formulation when carboxyterminated polybutadiene is used in place of hydroxyterminated polybutadiene.

We claim:

1. A composite propellant composition comprisin a cured intimate mixture of a metal additive of aluminum powder from about 1 to about 15 weight percent, ammonium perchlorate oxidizer from about 58 to about 80 weight percent, binder selected from carboxy terminated polybutadiene and hydroxy terminated polybutadiene from about 6 to about 14 weight percent, a curing agent from about 1 to about 3 weight percent selected from a diaziridine and triaziridine for use with carboxy terminated polybutadiene binder and diisocyanate for use with hydroxy terminated polybutadiene binder, a coplasticizer isodecyl pelargonate from 0 to 5 weight percent, and a ballistic modifier from about 5 to about 14 weight percent, said ballistic modifier being an NF carborane having the structure:

2. The propellant composition of claim 1 and wherein said ballistic modifier is the NF carborane having the structure:

and said ballistic modifier is present in the amount of about 13.2 weight percent; and said curing agent is toluene diisocyanate which is added up to about 3 parts per 100 parts of the other combined propellant ingredients.

4. A composite propellant composition comprising a cured intimate mixture of a metal additive of aluminum powder from about 1 to about 15 weight percent; ammonium perchlorate oxidizer from about 58 to about 10 80 weight percent; a hydroxy terminated polybutadiene binder from about 6 to about 14 weight percent; a diiso cyanate curing agent from about 1 to about 3 weight percent; and a ballistic modifier being isobutylcarbonane from about 5 to about 14 weight percent.

5. The propellant composition of claim 4 and wherein said ammonium perchlorate has particle size of about 2.5 microns and is present in amount of about 73.0 weight percent; said binder is hydroxy terminated polybutadiene in an amount of about 10.6 weight percent; said curing agent is a diisocyanate in amount of about 2.4 weight percent; and said ballistic modifier is isobutylcarborane in an amount of about 12.0 weight percent.

References Cited UNITED STATES PATENTS 3,141,803 7/1964 Green et al. 149-22 X 3,152,190 10/1964 Schwartz et al. 149-22 X 3,360,569 12/ 1967 Grafstein et al. 14922 UX 3,137,719 6/1964 Papetti 260--448.2 3,245,849 4/1966 Klager et al. 149-19 3,308,170 3/1967 Pritchett et a1. 260-632 3,377,370 4/1969 Papetti 260-4482 3,386,869 6/1968 Green et al. 149-19 3,406,203 10/1968 Morrow et al. 260-583 3,440,292 4/ 1969 Allen 260-633 3,457,223 7/1969 Papetti 260-465 3,476,622 11/1969 Harada et a1 149-19 CARL D. QUARFORTH, Primary Examiner E. A. MILLER, Assistant Examiner 5 US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,7 4,417 Dated ber 9, 1973 w William E. Hill et al Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7 li ne 19, "Component: Wt.Percent" should read Pi"e ssure: Burning rate (in./sec.) Column 7, line 25, "Pressure: Burning rate in./sec.)" should read Component: Wt. percent".

Signed and sealed this 27th day of August 1974.

(SEAL) Attest: v v

. MCCOY M. GIBSON; JR. c. MARSHALL DANN Attesting Officerv Commissioner of Patents FORM po'wso I P Q v uscoMM-oc wave-pan I U.$. GOVERNMENT PRINTING OFFICE 1 IQI! O-BGG-SSL UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,754,417 Dated t er 9, 1973 William E. Hill et a1 Inventor(s) It is certified that error appears in the above-identified patent and that said LettersPat'ent are hereby corrected as shown below:

Column 7; iine 19, "Component: Wt.Percent" should read :Pre ssure: Burning rate (in./sec.) Column 7, 'line 25, "Pressure: Burning rate in./sec.)"

should read Component: Wt. percent".

Signed and sealed this 27th day of August 1974.

(SEAL) Attest:

MCCOY M. GIBSON;- JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents FORM P040 (1069) I Q i I USCOMM-DC 60S76-P69 U.S GOVERNMENT PRINTING OFFICE ISIS O3G6-33l, 

